Our goal is to determine the mechanism of abnormal brain function in severe liver disease. Toward this end we have two approaches: 1) to identify and isolate potentially toxic agents in the blood and spinal fluid of patients with hepatic coma, and 2) to examine the enzymes and substrates involved in cerebral ammonia metabolism in rats made acutely and chronically hyperammonemic. Cerebrospinal fluid of patients with demonstrated liver disease will be analyzed for concentrations of ammonia, glutamine, gamma-aminobutyrate, and alpha-ketoglutaramate (alpha-KGM). Particular attention will be devoted to establishing whether or not alpha-KGM in CSF a) are diagnostic of hepatic encephalopathy, b) correlate with the severity of neurological impairment, and c) when elevated, can exert a direct toxic action on the brain. Activities of the principal enzymes involved in the metabolism of ammonia-glutamine-alpha-ketoglutaramate (i.e., glutamic dehydrogenase, glutamine synthetase, glutamine transaminase, and omega-amidase) will be determined in post-mortem brain samples of hepatic and non-hepatic patients, and attempts will be made to purify the omega-amidase from human brain. As an experimental model of chronic hyperammonemia, rats will be prepared with a portacaval shunt and at intervals post-shunting they will be given an ammonia load to precipitate a "hepatic crisis." Brains of treated and control rats will be analyzed for concentrations of high-energy compounds, amino acids and ammonia, or examined histologically for presence of Alzheimer's glial cells. BIBLIOGRAPHIC REFERENCES: Lockwood, A.H., McDonald, J.M., Gelbard, A.S., Reiman, R.E., Duffy, T.E., Laughlin, J.S., and Plum, F.: Cerebral ammonia metabolism in liver disease in man. Clin. Research 24: 433A, l976. Gjedde, A., Lockwood, A.H., Duffy, T.E., and Plum, F.: Effect of ammonia on cerebral metabolism of rats with portacaval shunts. Arch. Neurol. 33: 392, l976.